CHEMISTRY. 
the body placed within it is cooled down to the tempera¬ 
ture of 32°. The capacities in this cafe are direftiy as 
the quantities c'f ice melted. The fine of thefe methods 
has been praftifed by Dr. Crawford. The fecond was 
contrived by Lavoifter and La Place. It is ftill a quef- 
tion among chemifts, whether the whole quantities of ca¬ 
loric contained in equal weights of different bodies, hav¬ 
ing the fame temperature, be-proportioned to the capa¬ 
cities of thefe bodies ? It has been-afeertained, that in 
many chemical changes, caloric diiappears, is'abforbed, 
or becomes Intent-, while, in the converfe of thefe chan¬ 
ges, precifely the fame quantity of caloric re-appears, is 
evolved, becomes free or fenfible. Thus, when n pound 
of ice at 32" is mixed with a pound of water at 167^, 
the ice is liquefied, but the temperature of the mixture 
continues at 32 0 ; that is, ice abforbs as much caloric in 
thawing, as would raife the temperature of an equal 
quantity of water 13 5 0 . In the fame manner, when wa¬ 
ter at ii2° is converted into fleam, the fleam abforbs 
as much caloric without having its temperature increaf- 
ed by it, as would raife tire temperature of an equal 
quantity of water 94.3°, if tire water were not converti¬ 
ble, at that temperature, into fleam. But the capacity 
of fleam for caloric, is greater than the capacity of wa¬ 
ter, and the capacity of water is greater than the capa¬ 
city of ice. Confequently, more caloric will be necef- 
fary, to give water the temperature of 32 0 , than to give 
ice the temperature of 32° ; and more'will be required 
to give fleam the temperature of 212 0 , than to give wa¬ 
ter the temperature of 212 0 . It may then be queftion- 
ed, whether the whole caloric that difappears in the melt¬ 
ing of ice, and in the converfion of water into fleam, 
has been abforbed by the water and fleam refpeftively, 
in confequence of their change of capacity r Or, whe¬ 
ther fome part of it has net been chemically united with 
the water and fream refpeftively, in fuch a manner as 
not to affeft their temperatures? Dr. Crawford in-> 
clines to the former of thefe hypothefes ; the French che- 
miils aredifpofed to admit the latter. 
It is principally with the view of determining whether 
the fpecific caloric of bodies be proportioned to their ca¬ 
pacities, that the inquiry after the real zero, or point of 
total privation, has been purfued. It is taken for grant¬ 
ed, in this inquiry, that whenever caloric is abforbed or 
evolved by a lyftem of bodies, the quantity abforbed or 
evolved has the fame ratio to the whole caloric exifting 
in the fyflem after the experiment is concluded, which 
the difference between the former.and prefent capacity of 
the fyflem has to its prefent capacity. An example v/ill 
illuftrate the manner in which the real zero is calculated 
from thefe principles. When ice is converted into wa¬ 
ter, its capacity is increafed in the ratio of nine to ten, 
according to Kirwan ; and as much caloric is abforbed, 
according to La Place, as would be fufficient to raife the 
temperature of water 135 0 . Let us fuppofe that the 
whole of this abforption depends on the change of capa-. 
city in the ice; it will follow, that i-roth of the whole 
caloric contained in water at 32 0 , is fufficient to main¬ 
tain the temperature of the water at 135°; and, confe¬ 
quently, the remaining 9-iotbs will be able to maintain 
its temperature, 135 0 x 9 0 =:i2i5 o . That is, the whole 
caloric contained in water at 32 0 , is fufficient to com¬ 
municate the temperature of i3 5o p to a body, having the 
fame capacity with water; and therefore theabfolute ze¬ 
ro, or point of total privation, as determined by this cal¬ 
culation, is 1328° below o of Fahrenheit’s feale. 
When we confiderthe expanfive power of caloric, and 
its conlequent tendency to the flate of equilibrium, it is 
evident that the real zero, or point of total privation, 
mull be the fame in bodies of every kind; and the pre¬ 
ceding calculation will therefore conduct us, in every 
infiance, to the fame point, provided the principles on 
which it is founded arejufl, and provided the neceffary 
experiments have been made with accuracy. It is in this 
view, that the inquiry after the real zero, ferves to uf- 
Yol. IV, No. 1880 
185 
certain whether the hypothecs be true, that the fpecific 
caloric of bodies is proportioned to their capacities. 
For, if different experiments fhall, without exception, 
indicate the fame po;nt, as the abfolute zero, it may be 
inferred, that the liypothefis in queftion is juft; and, on 
the contrary, if the conclufions from different experi¬ 
ments (hall difagree, and if their differences be greater 
than what may be reafonably allowed for, on account of 
the difficulty of conducting experiments of fo great nice¬ 
ty, it may be inferred, that the fpecific caloric of bodies 
is not proportioned to their capacities ; that the abforp- 
tion and evolution of caloric, in different proceffes, de¬ 
pend not entirely upon the changes of capacity in the 
f’ubftances employed, but, in fome meafure, on the en¬ 
trance of caloric into chemical combination. The expe¬ 
riments that have been hitherto made, to afeertain the 
real zero, are not fufficiently numerous, nor fufficiently 
free from objeftions, to authorife either of the preceding 
conclufions, though they are infinitely more favourable 
to the latter than to the former. 
The diffufion of caloric among a fyflem of bodies, 
which was thought analogous to motion, feems to de¬ 
pend on two caufes; on their refpeftive capacities for 
caloric, and on their refpeftive conducting powers. M. 
PiCtet has illuftrated the manner in which thefe caufes 
co-operate, with Angular perfpicuity. It is impoflible 
to place the fubjeft in a clearer point of view than by a 
free tranflation from his work. Let us fuppofe a focus, 
from which flows a conflant and uniform ftream of calo¬ 
ric; and let us place at equal diflances from this focus, 
and connected with it by the fame medium, a number of 
bodies, having the fame nature, and the fame magni¬ 
tude. Thefe bodies will be filled with caloric in the fame 
manner, their temperatures will rife bjr fimilar grada¬ 
tions, and will ceafe to rife when the caloric they con¬ 
tain fhall have acquired an expanfive power fuflicient to 
refift the introduction of more caloric from the focus. 
But let us place at equal diflances from the fame focus, a 
number of bodies,' having the fame weight, and differing 
in their nature, fuch as a pound of water, a pound of 
glafs, a pound of mercury, &c. Thefe bodies will be 
filled with caloric as the former bodies were, and they 
will arrive at length at the fame common temperature, 
but in different times, and by diflimilar gradations. 
This difference will depend on the combination of two 
caufes. The one is, the different permeability of the bo¬ 
dies to caloric, or their different conduCling powers, in 
confequence of which caloric will take a longer or fhort- 
er time to penetrate their fubflance. The other is, the 
different capacities of the bodies for caloric, in confe¬ 
quence of which they will require unequal quantities of 
free caloric to arrive at the fame common temperature ; 
that is, to the flate in which the free caloric of the whole 
fyflem of bodies tends to expand itfelf with the fame force. 
We have little accurate information refpefting the 
permeability of bodies to caloric. We owe to Dr. Frank¬ 
lin the obfervation, that the non-conduftors of electrici¬ 
ty are alfo bad condudtors of caloric, and that the belt 
conductors of eleftricity are alfo excellent conductors of 
caloric. We have examples of this analogy between the 
eleCtric fktid and caloric, in metals upon the one hand, 
and in glafs and refinous fubflances on the other. 
But this rule is liable to many exception's. The com¬ 
mon torriceliian vacuum affords a ready paffage to the 
eleClric fluid; but Sir B. Tbompfon found, that it was 
lefs permeable to caloric than atmofpheric air, which 
itfelf is a very bad conduCror of caloric. Sulphur and 
oils, which are non-conduftors of eleftricity, are repre- 
fented by Humboldt as among the bed conductors of ca¬ 
loric. In order to conflruft a table of the permeability of 
bodies to caloric, it would be necefl'ary to know the times 
during which equal weights of different bodies acquire 
the kune increafe of temperature when expofed to equal 
calorific caufes, or fultain the fame lofs of temperature 
when expofed to equal cooling caufes. It would 
3 B be 
